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Using a Computational Galvanic Model in a Fracture Mechanics Framework to Improve Material Degradation Prediction 

By Thomas Curtin, Robert Adey, Andres Peratta, John Baynham

Although computational methods have been separately developed to predict corrosion and fatigue crack growth rates for metallic structures, challenges remain in implementing a methodology that considers the combined effects.  In this work the output from a galvanic model is used to determine the spatial distribution of corrosion damage; providing a guide for the location of discrete corrosion damage features that can be analyzed using stress fields from structural models.

In order to build confidence in this approach the galvanic models are validated by comparing predicted results to surface damage measurements from test specimens subject to ambient atmospheric exposure.  There was good comparison between the predicted spatial distribution of corrosion damage and the measured surface damage profiles obtained from the galvanic test specimens.

Following this exercise novel computational corrosion damage features were developed to represent simplified crack shapes emanating from corrosion pits. Stress intensity factors (SIF) for these newly developed hybrid pit-crack features were determined and these solutions compared to cases where the pit is assumed to be an equivalent crack.  The impact of the local, cavity induced stress field, on the SIF solutions is discussed.

Building on these findings a fatigue crack growth simulation was performed using an initial flaw emanating from a hemispherical cavity (corrosion pit) located at the edge of hole in a plate. A reasonable comparison of the predicted number of crack growth cycles to available experimental test results was achieved.

Predicted corrosion penetration

Crack growth progression for initial corner flaw growing from a pit

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